Many known absorbent articles such as diapers, incontinence articles, feminine hygiene products, and training pants, typically comprise absorbent core materials located between a liquid pervious body-side liner or topsheet and a vapor permeable, liquid impermeable outer cover or backsheet. The bodyside liner allows bodily liquids to flow through easily and towards the absorbent core. The absorbent core takes up the liquids quickly. Thus, no excessive pooling of liquids occurs on the body-facing surface of the absorbent article. The outer cover is typically liquid impermeable such that there would be no leakage from the absorbent article. However, because the disposable absorbent article may be worn for hours, sometimes after the absorbent article has taken up liquids, perspiration from the wearer's body, and liquid vapors escaped from the absorbent core, can get entrapped in the space between the absorbent article and the wearer's skin, resulting in an increased relative humidity in the occluded area. As is known in the art, the increased relative humidity leads to discomfort and overhydrated skin, which is prone to skin health problems, especially rashes and other contact dermatitis.
Generally, liquid impermeable backsheets are well suited to prevent the leakage of bodily fluids (such as urine, menses or fecal matters) from the absorbent material to the outer garment of a wearer. However, the use of such an impermeable backsheet can result in a high degree of humidity in the absorbent article when the absorbent article is in use such that a relatively elevated skin hydration levels may result.
The problem of high relative humidity near the skin in an absorbent article has been addressed in the art through a number of means. For example, U.S. Pat. No. 5,137,525 uses mechanical means to increase airflow in the article. Alternatively, breathable outer cover having microporous or monolithic films may be used in an absorbent article to allow air and water vapor diffusion. PCT Publications WO 98/58609 discloses absorbent article using other water vapor permeability, liquid impermeable barrier materials as the backsheet. PCT Publication WO 00/10497, WO 00/10498, WO 00/10499, WO 00/10500, WO 00/10501 relate to breathable absorbent articles exhibiting the several properties of the dry and wet articles. The absorbent articles disclosed in these publications typically have high permeability zones within the absorbent core, for, example, by aperturing the absorbent core or by varying high absorbency material content in portions of the core. However, the absorbent articles include microporous backsheets through which the moisture vapor diffuses from the inside to the outside of the absorbent articles. The diffusion mechanism is not very effective in removing moisture vapor. Thus, when the absorbent article is loaded with large amount of liquids, such as urine, the ineffectiveness of the diffusion through a backsheet may result in significantly increased relative humidity between the skin of the wearer and the article.
Another performance parameter of interest for the loaded/wet absorbent article is its ability to hold the liquid and prevent leakage especially when the article is subjected to pressure or impact force applied by wearer's motion, such as sitting, walking, bending, and falling. The leakage under impact or pressure becomes a serious problem when the absorbent article is loaded with liquids to near its absorbent capacity. Consequently, it is desirable to have an absorbent article which exhibits a balance of properties—on one hand it is desirable to keep the relative humidity in the space between the wearer and the absorbent article (i.e., the “local” environment) in a comfortable range, typically between about 30% to about 70% and more typically between about 30% to about 50% relative humidity. Further, the absorbent article should desirably have the ability to hold liquids without leakage, especially when the article is heavily loaded (i.e., at or near its absorbent capacity). It is also desirable to provide an absorbent article which manages the relative humidity level within the “local” (i.e., the space between the wearer and the absorbent article) environment by a convective transport mechanism. It is further desirable to provide an absorbent article having a carefully designed combination of chassis elements such that the “local” conditions (e.g., relative humidity, skin temperature) are optimized for maintaining or improving skin health.
Typically, to reduce the humidity level within the space between the absorbent article and the wearer's skin, breathable polymer films have been used as the outer cover for the absorbent article. The breathable films are typically constructed with micropores to provide substantial liquid impermeability and some diffusive air/vapor permeability.
Other disposable absorbent articles have been designed to provide breathable regions in the form of breathable panels or perforated openings in the backsheet or in the core to help ventilate the garment. Articles using perforated components or breathable panels often exhibit excessive leakage or wet-through of liquids from the article. Moreover, the wearer's movements (e.g., sitting, falling, walking, lying) may subject the absorbent article to physical forces, such as impact, compression, bending and the like, which may lead to increased leakage and wet-through. The leakage/wet-through problem becomes more severe under higher impact or pressure, heavy discharges and/or extended wear time.
Alternatively, multi-layered backsheets or outer covers have been used to address the wet-through problem. For example, breathable materials such as a fibrous textile or a nonwoven web have been used in the outer cover, either alone or in laminates with the microporous film. The relatively open structures of such materials allow air or vapor to diffuse through easily. The laminates may provide improved liquid impermeability and diffusive air/vapor permeability. The materials may be treated to further improve the liquid impermeability. However, the laminates still do not provide satisfactory protection against wet through under impact and/or sustained pressure. Further, the transport of air or vapor through the laminates via a diffusive mechanism is not as effective as the transport via a convective mechanism.
An alternative approach to the wet-through problem is to improve the absorbent material such that little or no liquid comes into contact with the backsheet, thereby preventing wet-through. This is typically achieved by increasing the amount of absorbent material in the article. However, this approach may lead to an increase in thickness of the article and a decrease in comfort as well as a decrease in vapor/air permeability through the article.
Another approach to the wet-through problem is to place formed films between the core and the backsheet. Formed films having apertures in the shape of slanted cones are disclosed in PCT publications WO 99/39672, WO 99/39673 and WO 99/39674. However, after compaction or sustained pressure, these formed films fail to maintain their formed shape; consequently, they fail to provide the desired balance of properties. The compaction or sustained pressure condition may occur before consumer use (e.g., during packaging, shipping, and storage), or during use (e.g., when the wearer sits or falls on the absorbent article).
Therefore, it is desirable to have absorbent articles that provide consumer comfort, in terms of reduced relative humidity within the absorbent article at a desirable overall thickness, and still achieve satisfactory wet-through protection.
It is also desirable to provide absorbent articles which manage the relative humidity within the space between the article and the wearer's skin to maintain good skin health. Further, it is desirable to manage the relative humidity within the absorbent article by an effective convective transport mechanism, and, optionally some degree of diffusive transport mechanism may be incorporated as well.
Additionally, it is desirable to provide absorbent articles wherein an optimal local i.e., within the space between the article and the wearer's skin) condition for skin health and wearer comfort is achieved by careful designs of components of the article. Specifically, it is desirable to provide an absorbent barrier structure having the desired wet-through protection and air/vapor permeability. Further, the absorbent barrier structure has a desirable thickness for wearer comfort.
It is desirable to provide absorbent articles comprising a barrier absorbent structure that can be exposed to compact and/or sustained pressure conditions for at least 24 hours without substantially degrading its performance, such as air permeability, liquid impermeability and resistance to leakage under impact or sustained pressure.